Liquid crystal on silicon display device having stacked integrated circuit substrates

Abstract

An example liquid crystal display device includes a reflective display backplane and one or more integrated circuit substrates arranged in a stacked configuration. The reflective display backplane includes an array of reflective pixel mirrors and a corresponding array of data latches. The top face of one integrated circuit substrate is connected to the back side of the reflective display backplane and is configured as a display driver, providing control signals to the reflective display backplane using a set of through-silicon-vias. Optionally, another integrated circuit substrate is connected (face-to-back) to the one integrated circuit substrate and is configured to provide virtual reality, augmented reality, and/or other video processing support to the display driver. An example embodiment is provided with a chip-scale-package structure formed on the bottom integrated circuit substrate of the stack.

We claim: 
     
         1 . A liquid crystal display device comprising:
 a first circuit substrate having a first surface, a second surface opposite said first surface, a first set of integrated circuits formed in and on said second surface of said first circuit substrate and including a first set of metal interconnect layers, and an array of conductive pixel mirrors formed over said first set of metal interconnect layers and electrically coupled to said circuits of said first set of integrated circuits via said first set of metal interconnect layers;   a second circuit substrate having a first surface, a second surface opposite said first surface, and a second set of integrated circuits formed in and on said second surface of said second circuit substrate and including a second set of metal interconnect layers;   a first set of conductive vias passing through said first circuit substrate and electrically connecting said first set of metal interconnect layers to said second set of metal interconnect layers;   a layer of liquid crystal material disposed over said array of conductive pixel mirrors; and   a transparent electrode disposed over said layer of liquid crystal material.   
     
     
         2 . The liquid crystal display device of  claim 1 , wherein said first set of metal interconnect layers includes at least one bond pad exposed on said first surface of said first circuit substrate. 
     
     
         3 . The liquid crystal display device of  claim 1 , further comprising:
 a chip scale packaging (CSP) structure having a first surface and a second surface opposite said first surface, said CSP structure including a first set of contacts formed on said first surface of said CSP structure and a second set of contacts formed on said second surface of said CSP structure; and   a second set of conductive vias passing through said second circuit substrate and electrically connecting said second set of metal interconnect layers to said first set of contacts.   
     
     
         4 . The liquid crystal display device of  claim 1 , further comprising:
 a third circuit substrate having a first surface, a second surface opposite said first surface, and a third set of integrated circuits formed in and on said second surface of said third circuit substrate and including a third set of metal interconnect layers; and   a second set of conductive vias passing through said second circuit substrate and electrically connecting said second set of metal interconnect layers to said third set of metal interconnect layers.   
     
     
         5 . The liquid crystal display device of  claim 4 , further comprising:
 a chip scale packaging (CSP) structure having a first surface and a second surface opposite said first surface, said CSP structure including a first set of contacts formed on said first surface of said CSP structure and a second set of contacts formed on said second surface of said CSP structure; and   a third set of conductive vias passing through said third circuit substrate and electrically connecting said third set of metal interconnect layers to said first set of contacts.   
     
     
         6 . The liquid crystal display device of  claim 4 , wherein:
 said first circuit substrate is a reflective display backplane including a data input and a control signal input;   said second set of integrated circuits includes a video data buffer and a control signal generator configured to generate control signals based on data stored in said data buffer and to provide said control signals to said control signal input of said reflective display backplane; and   said third set of integrated circuits includes video processing circuitry.   
     
     
         7 . The liquid crystal display device of  claim 6 , wherein said video processing circuitry includes:
 circuitry configured to receive video data of a first format; and   circuitry configured to convert said video data of said first format to video data of a second format.   
     
     
         8 . The liquid crystal display device of  claim 1 , wherein:
 said first set of integrated circuits includes a plurality of pixel latches, each pixel latch of said array of pixel latches being electrically coupled to an associated one of said conductive pixel mirrors; and   said second set of integrated circuits includes a frame buffer configured to store at least one frame of pixel data.   
     
     
         9 . The liquid crystal display device of  claim 8 , wherein said frame buffer has a capacity sufficient to store a plurality of frames of pixel data. 
     
     
         10 . The liquid crystal display device of  claim 1 , wherein:
 said first set of integrated circuits operate at a first voltage;   said second set of integrated circuits operate at a second voltage; and   said first voltage is higher than said second voltage.   
     
     
         11 . The liquid crystal display device of  claim 10 , further comprising interface circuitry whereby digital video data is transferred from said second set of integrated circuits operating at said second voltage to said first set of integrated circuits operating at said first voltage. 
     
     
         12 . The liquid crystal display device of  claim 1 , wherein:
 said first circuit substrate has a technology node of at least 65 nm; and   said second circuit substrate has a technology node of 28 nm or less.   
     
     
         13 . The liquid crystal display device of  claim 12 , wherein said first circuit substrate has a technology node of at least 130 nm. 
     
     
         14 . The liquid crystal display device of  claim 12 , wherein said second circuit substrate has a technology node of 22 nm or less. 
     
     
         15 . The liquid crystal display device of  claim 1 , wherein said second set of integrated circuits includes display driver circuits. 
     
     
         16 . The liquid crystal display device of  claim 15 , wherein said display driver circuits include control circuitry and memory. 
     
     
         17 . The liquid crystal display device of  claim 1 , further comprising:
 a dam surrounding said layer of liquid crystal material; and wherein   said first set of integrated circuits, said first set of metal interconnect layers, said second set of integrated circuits, and said second set of metal interconnect layers are all contained within a space defined by a perimeter of said dam projected along an axis perpendicular to said first surface of said first circuit substrate.   
     
     
         18 . A liquid crystal display device comprising:
 a first circuit substrate including a top surface, an opposite bottom surface, an array of pixel mirrors formed on said top surface, a first set of integrated circuits configured to assert pixel data on said pixel mirrors, and a plurality of electrical contacts formed on said bottom surface, said electrical contacts connected to said first set of integrated circuits;   a liquid crystal layer disposed over said pixel mirrors;   a transparent electrode disposed over said liquid crystal layer; and   a second circuit substrate including a top surface, a bottom surface opposite said top surface, a second set of electrical contacts formed on said top surface, and a second set of integrated circuits electrically coupled to said second set of electrical contacts, said second set of integrated circuits including a frame buffer configured to store digital video data and control circuitry configured to generate control signals based at least in part on said digital video data; and wherein   said first set of electrical contacts is rigidly connected to said second set of electrical contacts, thereby providing a mechanical bond between said first circuit substrate and said second circuit substrate, and providing an electrical connection over which said control signals are communicated from said second set of integrated circuits to said first set of integrated circuits.   
     
     
         19 . A method of manufacturing a liquid crystal display device, said method comprising:
 providing a reflective display backplane including an array of pixel mirrors;   forming vias through said reflective display backplane;   providing one or more integrated circuit substrates;   forming vias in said one or more integrated circuit substrates;   assembling said reflective display backplane and said one or more integrated circuit substrates in a stacked relationship with said reflective display backplane disposed between a cover glass and said one or more integrated circuit substrates;   electrically connecting circuitry of said reflective display backplane and said one or more integrated circuit substrates by said vias;   forming a chip-scale-package structure on a bottom one of said integrated circuit substrates; and   assembling liquid crystal display components over said array of pixel mirrors.